The primary objectives of this research are (1) to investigate the basic mechanisms by which masked and latent (M/L) viruses establish and maintain steady-state relationships with host cells; (2) to determine whether M/L viruses are present in normal human brain tissues; and (3) to determine whether M/L viruses are regularly associated with human brain tumors. We have chosen simian brain as a source of material for studying naturally occurring M/L viruses because of the high frequency with which such agents can be demonstrated in simian tissues and because the findings might have direct application to similar studies in man. Using this model, as well as human brain cultures, we will seek to determine the conditions most favorable for inducing emergence of M/L viruses and the most sensitive means by which viruses can be detected. New insights gained concerning the mechanisms for establishing and altering virus-cell equilibrium states, together with improvements in virus detection technology, will be applied to concurrent studies of normal and neoplastic human brain tissues. We will continue to develop a liquid nitrogen cell bank containing (1) virus-free brain cells, (2) cells containing identifiable, naturally occurring latent viruses, and (3) cells known to contain masked viruses. Multiple replicate samples of cells from many individuals will thus be perpetually available for repeated experimentation to determine optimal conditions for revealing and detecting M/L viruses. Normal and neoplastic human brain cells, similarly stored, will be available for revival and study at any convenient time by the most favorable means that can be devised. These means will include every technique for inducing virus emergence and for virus detection which the present state of knowledge would suggest. We will also study the phenomenon that certain types of brain tumors in humans induce tumor specific antibodies. We will seek to determine the significance of these antibodies in relation to regression or progression of tumors, success or failure in therapy and to determine whether a serological test for these antibodies would be of value for early diagnosis of cancer.